From 24f3ab010422d82ef7e7acf9682f003e73432aa5 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Thu, 12 Aug 2010 04:14:00 +0100
Subject: [PATCH] --- yaml --- r: 209155 b: refs/heads/master c:
 708e929513502fb050c0a3c3ee267cab5b056ded h: refs/heads/master i:   209153:
 c145a16be1f414caaec3572a6aa6cb681f53b601   209151:
 b53da4c4418e9c58e8c90eca9eee20e4f16ae227 v: v3

---
 [refs]                |  2 +-
 trunk/drivers/md/dm.c | 15 +++++++++++++--
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/[refs] b/[refs]
index 08923c2c20cd..cfb59e62d8d2 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 87c961cb747fa55b664b76abfcb9d44c14ae851f
+refs/heads/master: 708e929513502fb050c0a3c3ee267cab5b056ded
diff --git a/trunk/drivers/md/dm.c b/trunk/drivers/md/dm.c
index a503b95ecbfb..f3cc5d99fe8d 100644
--- a/trunk/drivers/md/dm.c
+++ b/trunk/drivers/md/dm.c
@@ -639,8 +639,14 @@ static void dec_pending(struct dm_io *io, int error)
 			 * There can be just one barrier request so we use
 			 * a per-device variable for error reporting.
 			 * Note that you can't touch the bio after end_io_acct
+			 *
+			 * We ignore -EOPNOTSUPP for empty flush reported by
+			 * underlying devices. We assume that if the device
+			 * doesn't support empty barriers, it doesn't need
+			 * cache flushing commands.
 			 */
-			if (!md->barrier_error && io_error != -EOPNOTSUPP)
+			if (!md->barrier_error &&
+			    !(bio_empty_barrier(bio) && io_error == -EOPNOTSUPP))
 				md->barrier_error = io_error;
 			end_io_acct(io);
 			free_io(md, io);
@@ -2284,7 +2290,12 @@ static void process_barrier(struct mapped_device *md, struct bio *bio)
 
 	if (!bio_empty_barrier(bio)) {
 		__split_and_process_bio(md, bio);
-		dm_flush(md);
+		/*
+		 * If the request isn't supported, don't waste time with
+		 * the second flush.
+		 */
+		if (md->barrier_error != -EOPNOTSUPP)
+			dm_flush(md);
 	}
 
 	if (md->barrier_error != DM_ENDIO_REQUEUE)